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Property, Plant, and Equipment - Reconciliation of the changes in the carrying amount of PP&E (Details) - CAD ($) $ in Millions | 12 Months Ended
--- | ---
Dec. 31, 2020 | Dec. 31, 2019 | Dec. 31, 2018
Disclosure of detailed information about property, plant and equipment [line items] |  |  |
Property, plant and equipment, beginning of the period | $ 6,207 | $ 6,164 |
(Impairment) reversals (Note 7) | 0 | (18) | $ (23)
Property, plant and equipment, end of the period | 5,822 | 6,207 | 6,164
Gross carrying amount |  |  |
Disclosure of detailed information about property, plant and equipment [line items] |  |  |
Property, plant and equipment, beginning of the period | 13,395 | 13,202 |
Additions | 486 | 522 |
Acquisitions | 1 | 439 |
Disposals | (5) | (704) |
(Impairment) reversals (Note 7) | (81) | 431 |
Retirement of assets | (58) | (201) |
Change in foreign exchange rates | (3) | (134) |
Transfers | (431) | (29) |
Property, plant and equipment, end of the period | 13,398 | 13,395 | 13,202
Gross carrying amount | IFRS 16 |  |  |
Disclosure of detailed information about property, plant and equipment [line items] |  |  |
Property, plant and equipment, beginning of the period |  | 108 |
Property, plant and equipment, end of the period |  |  | 108
Accumulated depreciation |  |  |
Disclosure of detailed information about property, plant and equipment [line items] |  |  |
Property, plant and equipment, beginning of the period | (7,188) | (7,038) |
Disposals | 2 | 439 |
(Impairment) reversals (Note 7) |  | (297) |
Retirement of assets | 51 | 190 |
Change in foreign exchange rates | (21) | (76) |
Transfers | (255) | (26) |
Depreciation | (717) | (630) |
Property, plant and equipment, end of the period | (7,576) | (7,188) | (7,038)
Accumulated depreciation | IFRS 16 |  |  |
Disclosure of detailed information about property, plant and equipment [line items] |  |  |
Property, plant and equipment, beginning of the period |  | (46) |
Property, plant and equipment, end of the period |  |  | (46)
Land |  |  |
Disclosure of detailed information about property, plant and equipment [line items] |  |  |
Property, plant and equipment, beginning of the period | 91 | 94 |
Property, plant and equipment, end of the period | 96 | 91 | 94
Land | Gross carrying amount |  |  |
Disclosure of detailed information about property, plant and equipment [line items] |  |  |
Property, plant and equipment, beginning of the period | 91 | 94 |
Additions | 0 | 0 |
Acquisitions | 0 | 0 |
Disposals | (2) | (2) |
(Impairment) reversals (Note 7) | (9) | 0 |
Retirement of assets | 0 | 0 |
Change in foreign exchange rates | (1) | (1) |
Transfers | 17 | 0 |
Property, plant and equipment, end of the period | 96 | 91 | 94
Land | Gross carrying amount | IFRS 16 |  |  |
Disclosure of detailed information about property, plant and equipment [line items] |  |  |
Property, plant and equipment, beginning of the period |  | 0 |
Property, plant and equipment, end of the period |  |  | 0
Land | Accumulated depreciation |  |  |
Disclosure of detailed information about property, plant and equipment [line items] |  |  |
Property, plant and equipment, beginning of the period | 0 | 0 |
Disposals | 0 | 0 |
(Impairment) reversals (Note 7) |  | 0 |
Retirement of assets | 0 | 0 |
Change in foreign exchange rates | 0 | 0 |
Transfers | 0 | 0 |
Depreciation | 0 | 0 |
Property, plant and equipment, end of the period | 0 | 0 | 0
Land | Accumulated depreciation | IFRS 16 |  |  |
Disclosure of detailed information about property, plant and equipment [line items] |  |  |
Property, plant and equipment, beginning of the period |  | 0 |
Property, plant and equipment, end of the period |  |  | 0
Coal generation |  |  |
Disclosure of detailed information about property, plant and equipment [line items] |  |  |
Property, plant and equipment, beginning of the period | 2,120 | 2,172 |
Property, plant and equipment, end of the period | 1,856 | 2,120 | 2,172
Coal generation | Gross carrying amount |  |  |
Disclosure of detailed information about property, plant and equipment [line items] |  |  |
Property, plant and equipment, beginning of the period | 6,116 | 5,937 |
Additions | 0 | 0 |
Acquisitions | 0 | 300 |
Disposals | (1) | (389) |
(Impairment) reversals (Note 7) | (69) | 448 |
Retirement of assets | (35) | (158) |
Change in foreign exchange rates | (37) | (63) |
Transfers | 142 | 103 |
Property, plant and equipment, end of the period | 6,137 | 6,116 | 5,937
Coal generation | Gross carrying amount | IFRS 16 |  |  |
Disclosure of detailed information about property, plant and equipment [line items] |  |  |
Property, plant and equipment, beginning of the period |  | 0 |
Property, plant and equipment, end of the period |  |  | 0
Coal generation | Accumulated depreciation |  |  |
Disclosure of detailed information about property, plant and equipment [line items] |  |  |
Property, plant and equipment, beginning of the period | (3,996) | (3,765) |
Disposals | 1 | 170 |
(Impairment) reversals (Note 7) |  | (297) |
Retirement of assets | 31 | 158 |
Change in foreign exchange rates | (35) | (52) |
Transfers | 0 | 10 |
Depreciation | (352) | (304) |
Property, plant and equipment, end of the period | (4,281) | (3,996) | (3,765)
Coal generation | Accumulated depreciation | IFRS 16 |  |  |
Disclosure of detailed information about property, plant and equipment [line items] |  |  |
Property, plant and equipment, beginning of the period |  | 0 |
Property, plant and equipment, end of the period |  |  | 0
Gas generation |  |  |
Disclosure of detailed information about property, plant and equipment [line items] |  |  |
Property, plant and equipment, beginning of the period | 771 | 836 |
Property, plant and equipment, end of the period | 659 | 771 | 836
Gas generation | Gross carrying amount |  |  |
Disclosure of detailed information about property, plant and equipment [line items] |  |  |
Property, plant and equipment, beginning of the period | 1,671 | 1,964 |
Additions | 0 | 0 |
Acquisitions | 1 | 0 |
Disposals | 0 | (260) |
(Impairment) reversals (Note 7) | 0 | 0 |
Retirement of assets | (12) | (26) |
Change in foreign exchange rates | 45 | (40) |
Transfers | (263) | 22 |
Property, plant and equipment, end of the period | 1,431 | 1,671 | 1,964
Gas generation | Gross carrying amount | IFRS 16 |  |  |
Disclosure of detailed information about property, plant and equipment [line items] |  |  |
Property, plant and equipment, beginning of the period |  | 0 |
Property, plant and equipment, end of the period |  |  | 0
Gas generation | Accumulated depreciation |  |  |
Disclosure of detailed information about property, plant and equipment [line items] |  |  |
Property, plant and equipment, beginning of the period | (900) | (1,128) |
Disposals | 0 | 255 |
(Impairment) reversals (Note 7) |  | 0 |
Retirement of assets | 10 | 23 |
Change in foreign exchange rates | 18 | (16) |
Transfers | (212) | (11) |
Depreciation | (76) | (77) |
Property, plant and equipment, end of the period | (772) | (900) | (1,128)
Gas generation | Accumulated depreciation | IFRS 16 |  |  |
Disclosure of detailed information about property, plant and equipment [line items] |  |  |
Property, plant and equipment, beginning of the period |  | 0 |
Property, plant and equipment, end of the period |  |  | 0
Renewable generation |  |  |
Disclosure of detailed information about property, plant and equipment [line items] |  |  |
Property, plant and equipment, beginning of the period | 2,290 | 2,125 |
Property, plant and equipment, end of the period | 2,176 | 2,290 | 2,125
Renewable generation | Gross carrying amount |  |  |
Disclosure of detailed information about property, plant and equipment [line items] |  |  |
Property, plant and equipment, beginning of the period | 3,574 | 3,286 |
Additions | 0 |  |
Acquisitions | 0 | 0 |
Disposals | 0 | 0 |
(Impairment) reversals (Note 7) | (2) | (2) |
Retirement of assets | (7) | (7) |
Change in foreign exchange rates | (14) | (17) |
Transfers | 33 | 319 |
Property, plant and equipment, end of the period | 3,592 | 3,574 | 3,286
Renewable generation | Gross carrying amount | IFRS 16 |  |  |
Disclosure of detailed information about property, plant and equipment [line items] |  |  |
Property, plant and equipment, beginning of the period |  | 7 |
Property, plant and equipment, end of the period |  |  | 7
Renewable generation | Accumulated depreciation |  |  |
Disclosure of detailed information about property, plant and equipment [line items] |  |  |
Property, plant and equipment, beginning of the period | (1,284) | (1,161) |
Disposals | 0 | 0 |
(Impairment) reversals (Note 7) |  | 0 |
Retirement of assets | 6 | 3 |
Change in foreign exchange rates | (4) | (4) |
Transfers | 0 | (3) |
Depreciation | (142) | (136) |
Property, plant and equipment, end of the period | (1,416) | (1,284) | (1,161)
Renewable generation | Accumulated depreciation | IFRS 16 |  |  |
Disclosure of detailed information about property, plant and equipment [line items] |  |  |
Property, plant and equipment, beginning of the period |  | (3) |
Property, plant and equipment, end of the period |  |  | (3)
Mining property and equipment |  |  |
Disclosure of detailed information about property, plant and equipment [line items] |  |  |
Property, plant and equipment, beginning of the period | 386 | 508 |
Property, plant and equipment, end of the period | 330 | 386 | 508
Mining property and equipment | Gross carrying amount |  |  |
Disclosure of detailed information about property, plant and equipment [line items] |  |  |
Property, plant and equipment, beginning of the period | 1,226 | 1,338 |
Additions | 0 | 0 |
Acquisitions | 0 | 0 |
Disposals | 0 | (34) |
(Impairment) reversals (Note 7) | 0 | (15) |
Retirement of assets | (3) | (10) |
Change in foreign exchange rates | (2) | (3) |
Transfers | (29) | 25 |
Property, plant and equipment, end of the period | 1,268 | 1,226 | 1,338
Mining property and equipment | Gross carrying amount | IFRS 16 |  |  |
Disclosure of detailed information about property, plant and equipment [line items] |  |  |
Property, plant and equipment, beginning of the period |  | 101 |
Property, plant and equipment, end of the period |  |  | 101
Mining property and equipment | Accumulated depreciation |  |  |
Disclosure of detailed information about property, plant and equipment [line items] |  |  |
Property, plant and equipment, beginning of the period | (840) | (830) |
Disposals | 0 | 14 |
(Impairment) reversals (Note 7) |  | 0 |
Retirement of assets | 4 | 6 |
Change in foreign exchange rates | (2) | (2) |
Transfers | (29) | (22) |
Depreciation | (133) | (97) |
Property, plant and equipment, end of the period | (938) | (840) | (830)
Mining property and equipment | Accumulated depreciation | IFRS 16 |  |  |
Disclosure of detailed information about property, plant and equipment [line items] |  |  |
Property, plant and equipment, beginning of the period |  | (43) |
Property, plant and equipment, end of the period |  |  | (43)
Assets under construction |  |  |
Disclosure of detailed information about property, plant and equipment [line items] |  |  |
Property, plant and equipment, beginning of the period | 228 | 200 |
Property, plant and equipment, end of the period | 495 | 228 | 200
Assets under construction | Gross carrying amount |  |  |
Disclosure of detailed information about property, plant and equipment [line items] |  |  |
Property, plant and equipment, beginning of the period | 228 | 200 |
Additions | 478 | 407 |
Acquisitions | 0 | 139 |
Disposals | 0 | 0 |
(Impairment) reversals (Note 7) | 0 | 0 |
Retirement of assets | 0 | 0 |
Change in foreign exchange rates | 0 | (4) |
Transfers | (211) | (514) |
Property, plant and equipment, end of the period | 495 | 228 | 200
Assets under construction | Gross carrying amount | IFRS 16 |  |  |
Disclosure of detailed information about property, plant and equipment [line items] |  |  |
Property, plant and equipment, beginning of the period |  | 0 |
Property, plant and equipment, end of the period |  |  | 0
Assets under construction | Accumulated depreciation |  |  |
Disclosure of detailed information about property, plant and equipment [line items] |  |  |
Property, plant and equipment, beginning of the period | 0 | 0 |
Disposals | 0 | 0 |
(Impairment) reversals (Note 7) |  | 0 |
Retirement of assets | 0 | 0 |
Change in foreign exchange rates | 0 | 0 |
Transfers | 0 | 0 |
Depreciation | 0 | 0 |
Property, plant and equipment, end of the period | 0 | 0 | 0
Assets under construction | Accumulated depreciation | IFRS 16 |  |  |
Disclosure of detailed information about property, plant and equipment [line items] |  |  |
Property, plant and equipment, beginning of the period |  | 0 |
Property, plant and equipment, end of the period |  |  | 0
Capital spares and other |  |  |
Disclosure of detailed information about property, plant and equipment [line items] |  |  |
Property, plant and equipment, beginning of the period | 321 | 229 |
Property, plant and equipment, end of the period | 210 | 321 | 229
Capital spares and other | Gross carrying amount |  |  |
Disclosure of detailed information about property, plant and equipment [line items] |  |  |
Property, plant and equipment, beginning of the period | 489 | 383 |
Additions | 8 | 115 |
Acquisitions | 0 | 0 |
Disposals | (2) | (19) |
(Impairment) reversals (Note 7) | (1) | 0 |
Retirement of assets | (1) | 0 |
Change in foreign exchange rates | 6 | (6) |
Transfers | (120) | 16 |
Property, plant and equipment, end of the period | 379 | 489 | 383
Capital spares and other | Gross carrying amount | IFRS 16 |  |  |
Disclosure of detailed information about property, plant and equipment [line items] |  |  |
Property, plant and equipment, beginning of the period |  | 0 |
Property, plant and equipment, end of the period |  |  | 0
Capital spares and other | Accumulated depreciation |  |  |
Disclosure of detailed information about property, plant and equipment [line items] |  |  |
Property, plant and equipment, beginning of the period | (168) | (154) |
Disposals | 1 | 0 |
(Impairment) reversals (Note 7) |  | 0 |
Retirement of assets | 0 | 0 |
Change in foreign exchange rates | 2 | (2) |
Transfers | (14) | 0 |
Depreciation | (14) | (16) |
Property, plant and equipment, end of the period | (169) | (168) | (154)
Capital spares and other | Accumulated depreciation | IFRS 16 |  |  |
Disclosure of detailed information about property, plant and equipment [line items] |  |  |
Property, plant and equipment, beginning of the period |  | 0 |
Property, plant and equipment, end of the period |  |  | $ 0
Decommissioning and restoration | Gross carrying amount |  |  |
Disclosure of detailed information about property, plant and equipment [line items] |  |  |
Revisions and additions to decommissioning and restoration costs (Note 23) | 94 | (23) |
Decommissioning and restoration | Land | Gross carrying amount |  |  |
Disclosure of detailed information about property, plant and equipment [line items] |  |  |
Revisions and additions to decommissioning and restoration costs (Note 23) | 0 | 0 |
Decommissioning and restoration | Coal generation | Gross carrying amount |  |  |
Disclosure of detailed information about property, plant and equipment [line items] |  |  |
Revisions and additions to decommissioning and restoration costs (Note 23) | 21 | (62) |
Decommissioning and restoration | Gas generation | Gross carrying amount |  |  |
Disclosure of detailed information about property, plant and equipment [line items] |  |  |
Revisions and additions to decommissioning and restoration costs (Note 23) | (11) | 11 |
Decommissioning and restoration | Renewable generation | Gross carrying amount |  |  |
Disclosure of detailed information about property, plant and equipment [line items] |  |  |
Revisions and additions to decommissioning and restoration costs (Note 23) | 8 | 2 |
Decommissioning and restoration | Mining property and equipment | Gross carrying amount |  |  |
Disclosure of detailed information about property, plant and equipment [line items] |  |  |
Revisions and additions to decommissioning and restoration costs (Note 23) | 76 | 26 |
Decommissioning and restoration | Assets under construction | Gross carrying amount |  |  |
Disclosure of detailed information about property, plant and equipment [line items] |  |  |
Revisions and additions to decommissioning and restoration costs (Note 23) | 0 | 0 |
Decommissioning and restoration | Capital spares and other | Gross carrying amount |  |  |
Disclosure of detailed information about property, plant and equipment [line items] |  |  |
Revisions and additions to decommissioning and restoration costs (Note 23) | $ 0 | $ 0 |

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- Definition The increase in property, plant and equipment resulting from acquisitions through business combinations. [Refer: Business combinations [member]; Property, plant and equipment] + References Reference 1: http://www.xbrl.org/2003/role/disclosureRef -Name IAS -Number 16 -IssueDate 2019-01-01 -Paragraph 73 -Subparagraph e -Clause iii -URI http://eifrs.ifrs.org/eifrs/xifrs-link?type=IAS&num=16&code=ifrs-tx-2019-en-r&anchor=para_73_e_iii&doctype=Standard -URIDate 2019-03-27 + Details
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- Definition The amount of additions to property, plant and equipment other than those acquired through business combinations. [Refer: Business combinations [member]; Property, plant and equipment] + References Reference 1: http://www.xbrl.org/2003/role/disclosureRef -Name IAS -Number 16 -IssueDate 2019-01-01 -Paragraph 73 -Subparagraph e -Clause i -URI http://eifrs.ifrs.org/eifrs/xifrs-link?type=IAS&num=16&code=ifrs-tx-2019-en-r&anchor=para_73_e_i&doctype=Standard -URIDate 2019-03-27 + Details
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- Definition The amount of depreciation of property, plant and equipment. [Refer: Depreciation and amortisation expense; Property, plant and equipment] + References Reference 1: http://www.xbrl.org/2003/role/disclosureRef -Name IAS -Number 16 -IssueDate 2019-01-01 -Paragraph 73 -Subparagraph e -Clause vii -URI http://eifrs.ifrs.org/eifrs/xifrs-link?type=IAS&num=16&code=ifrs-tx-2019-en-r&anchor=para_73_e_vii&doctype=Standard -URIDate 2019-03-27 Reference 2: http://www.xbrl.org/2003/role/disclosureRef -Name IAS -Number 16 -IssueDate 2019-01-01 -Paragraph 75 -Subparagraph a -URI http://eifrs.ifrs.org/eifrs/xifrs-link?type=IAS&num=16&code=ifrs-tx-2019-en-r&anchor=para_75_a&doctype=Standard -URIDate 2019-03-27 + Details
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- Definition The decrease in property, plant and equipment resulting from disposals. [Refer: Property, plant and equipment] + References Reference 1: http://www.xbrl.org/2003/role/disclosureRef -Name IAS -Number 16 -IssueDate 2019-01-01 -Paragraph 73 -Subparagraph e -Clause ii -URI http://eifrs.ifrs.org/eifrs/xifrs-link?type=IAS&num=16&code=ifrs-tx-2019-en-r&anchor=para_73_e_ii&doctype=Standard -URIDate 2019-03-27 + Details
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- Definition The increase (decrease) in property, plant and equipment resulting from net exchange differences arising on the translation of the financial statements from the functional currency into a different presentation currency, including the translation of a foreign operation into the presentation currency of the reporting entity. [Refer: Property, plant and equipment] + References Reference 1: http://www.xbrl.org/2003/role/disclosureRef -Name IAS -Number 16 -IssueDate 2019-01-01 -Paragraph 73 -Subparagraph e -Clause viii -URI http://eifrs.ifrs.org/eifrs/xifrs-link?type=IAS&num=16&code=ifrs-tx-2019-en-r&anchor=para_73_e_viii&doctype=Standard -URIDate 2019-03-27 + Details
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- Definition The increase (decrease) in property, plant and equipment resulting from changes that the entity does not separately disclose in the same statement or note. [Refer: Property, plant and equipment] + References Reference 1: http://www.xbrl.org/2003/role/disclosureRef -Name IAS -Number 16 -IssueDate 2019-01-01 -Paragraph 73 -Subparagraph e -Clause ix -URI http://eifrs.ifrs.org/eifrs/xifrs-link?type=IAS&num=16&code=ifrs-tx-2019-en-r&anchor=para_73_e_ix&doctype=Standard -URIDate 2019-03-27 + Details
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- Definition The amount of tangible assets that: (a) are held for use in the production or supply of goods or services, for rental to others, or for administrative purposes; and (b) are expected to be used during more than one period. + References Reference 1: http://www.xbrl.org/2003/role/disclosureRef -Name IAS -Number 16 -IssueDate 2019-01-01 -Paragraph 73 -Subparagraph e -URI http://eifrs.ifrs.org/eifrs/xifrs-link?type=IAS&num=16&code=ifrs-tx-2019-en-r&anchor=para_73_e&doctype=Standard -URIDate 2019-03-27 Reference 2: http://www.xbrl.org/2003/role/disclosureRef -Name IAS -Number 1 -IssueDate 2019-01-01 -Paragraph 54 -Subparagraph a -URI http://eifrs.ifrs.org/eifrs/xifrs-link?type=IAS&num=1&code=ifrs-tx-2019-en-r&anchor=para_54_a&doctype=Standard -URIDate 2019-03-27 + Details
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